U.S. patent application number 13/891622 was filed with the patent office on 2014-11-13 for air handling constructions with turbo-compounding for opposed-piston engines.
This patent application is currently assigned to ACHATES POWER, INC.. The applicant listed for this patent is ACHATES POWER, INC.. Invention is credited to Nishit Nagar, Suramya D. Naik.
Application Number | 20140331656 13/891622 |
Document ID | / |
Family ID | 51033490 |
Filed Date | 2014-11-13 |
United States Patent
Application |
20140331656 |
Kind Code |
A1 |
Nagar; Nishit ; et
al. |
November 13, 2014 |
Air Handling Constructions With Turbo-Compounding For
Opposed-Piston Engines
Abstract
An opposed-piston engine has an air handling system equipped
with a turbo-compound system that includes a power turbine for
producing a rotary output in response to a flow of exhaust gas
flowing into the turbine. The rotary output is connected to a
crankshaft or other rotating element of the opposed-piston engine
for converting some of the exhaust gas energy into mechanical
energy supplied to the crankshaft.
Inventors: |
Nagar; Nishit; (San Diego,
CA) ; Naik; Suramya D.; (San Diego, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ACHATES POWER, INC.; |
|
|
US |
|
|
Assignee: |
ACHATES POWER, INC.
San Diego
CA
|
Family ID: |
51033490 |
Appl. No.: |
13/891622 |
Filed: |
May 10, 2013 |
Current U.S.
Class: |
60/297 ;
123/51R |
Current CPC
Class: |
F02B 25/08 20130101;
F02B 29/0412 20130101; F02B 41/10 20130101; F01B 7/14 20130101;
F02M 26/23 20160201; Y02T 10/146 20130101; Y02T 10/12 20130101;
Y02T 10/163 20130101; F02B 75/28 20130101; F02M 26/08 20160201 |
Class at
Publication: |
60/297 ;
123/51.R |
International
Class: |
F02B 75/28 20060101
F02B075/28 |
Claims
1. An opposed-piston engine, comprising: at least one cylinder with
exhaust and intake ports; a charge air channel to provide charge
air to at least one intake port; an exhaust channel to receive
exhaust from at least one exhaust port; a supercharger operable to
pump charge air in the charge air channel; and, a blowdown turbine
having a first turbine input coupled to receive exhaust gas from
the exhaust channel and a rotary output drivingly coupled to a
rotating element of the engine.
2. The opposed-piston engine of claim 1, in which the engine
includes an exhaust gas recirculation (EGR) loop having a loop
input coupled to the exhaust channel and a loop output coupled to
the charge air channel.
3. The opposed-piston engine of claim 2, in which the rotating
element is one of a gear train and an electrical converter.
4. The opposed-piston engine of claim 2, in which the engine
includes two crankshafts coupled by a gear train and the rotating
element is one of the crankshafts.
5. The opposed-piston engine of claim 2, in which the engine
includes a turbocharger with a charge air output coupled to the
charge air channel, a second turbine input coupled to the exhaust
channel, and a turbine output, and the first turbine input is
coupled to the turbine output.
6. The opposed-piston engine of claim 5, in which the rotating
element is one of a gear train and an electrical converter.
7. The opposed-piston engine of claim 2, in which the engine
includes two crankshafts coupled by a gear train and the rotating
element is one of the crankshafts.
8. The opposed-piston engine of claim 2, in which the engine
includes a turbocharger with a charge air output coupled to the
charge air channel, a second turbine input coupled to the exhaust
channel, and a turbine output, and the first turbine input is
coupled to the exhaust channel in common with the second turbine
input.
9. The opposed-piston engine of claim 8, in which the rotating
element is one of a gear train and an electrical converter.
10. The opposed-piston engine of claim 8, in which the engine
includes two crankshafts coupled by a gear train and the rotating
element is one of the crankshafts.
11. The opposed-piston engine of claim 2, in which the engine
includes no turbocharger.
12. The opposed-piston engine of claim 1, in which the engine
includes no turbocharger.
13. The opposed-piston engine of claim 12, in which the engine
includes no exhaust gas recirculation (EGR) loop.
14. The opposed-piston engine of claim 1, the engine further
comprising an after treatment arrangement including one or more of
a diesel oxidation catalyst device, a selective catalytic reduction
device, and a diesel particulate filter device arranged in a
sequence following a turbine output of the blowdown turbine.
15. An opposed-piston engine, comprising: at least one cylinder
with exhaust and intake ports; a charge air channel to provide
charge air to at least one intake port; an exhaust channel to
receive exhaust gas from at least one exhaust port; a supercharger
operable to pump charge air in the charge air channel; a blowdown
turbine having a first turbine input coupled to receive exhaust gas
from the exhaust channel and a rotary output drivingly coupled to a
rotating element of the engine; a bypass valve in the exhaust
channel operable to regulate a flow of exhaust gas through the
blowdown turbine; and, a control mechanization operable to control
the bypass valve in response to air management inputs and engine
operating conditions.
16. The opposed-piston engine of claim 15, in which the engine
includes an exhaust gas recirculation (EGR) loop having a loop
input coupled to the exhaust channel and a loop output coupled to
the charge air channel, and the control mechanization is operable
to control the supercharger, the EGR loop, and the bypass valve in
response to engine operating conditions.
17. The opposed-piston engine of claim 16, in which the rotating
element is one of a gear train and an electrical converter.
18. The opposed-piston engine of claim 16, in which the engine
includes two crankshafts coupled by a gear train and the rotating
element is one of the crankshafts.
19. The opposed-piston engine of claim 16, in which the engine
includes a turbocharger with a charge air output coupled to the
charge air channel, a second turbine input coupled to the exhaust
channel, and a turbine output, and the first turbine input is
coupled to the turbine output.
20. The opposed-piston engine of claim 19, in which the rotating
element is one of a gear train and an electrical converter.
21. The opposed-piston engine of claim 16, in which the engine
includes two crankshafts coupled by a gear train and the rotating
element is one of the crankshafts.
22. The opposed-piston engine of claim 16, in which the engine
includes a turbocharger with a charge air output coupled to the
charge air channel, a second turbine input coupled to the exhaust
channel, and a turbine output, and the first turbine input is
coupled to the exhaust channel in parallel with the second turbine
input.
23. The opposed-piston engine of claim 22, in which the rotating
element is one of a gear train and an electrical converter.
24. The opposed-piston engine of claim 22, in which the engine
includes two crankshafts coupled by a gear train and the rotating
element is one of the crankshafts.
25. The opposed-piston engine of claim 15, the engine further
comprising an after treatment arrangement including one or more of
a diesel oxidation catalyst device, a selective catalytic reduction
device, and a diesel particulate filter device arranged in a
sequence following a turbine output of the blowdown turbine.
26. A method of operating an opposed-piston engine, comprising:
generating exhaust gas in at least one ported cylinder of the
engine; transporting exhaust gas from an exhaust port of the ported
cylinder through an exhaust channel; recirculating a portion of the
exhaust gas from the exhaust channel; pressurizing fresh air;
mixing recirculated exhaust gas with the pressurized fresh air to
form charge air; pressurizing the charge air; providing the charge
air through an intake port of the ported cylinder; converting a
portion of the exhaust gas to rotary mechanical motion in a
blowdown turbine; and, coupling the rotary mechanical motion of the
blowdown turbine to a rotating element of the engine.
27. The method of claim 26, further comprising controlling engine
exhaust pressure by regulating the portion of exhaust gas converted
to rotary motion in response to engine air management conditions
and engine operating conditions.
28. The method of claim 26, further comprising controlling one of
mass flow and pressure drop by regulating the portion of exhaust
gas converted to rotary motion in response to engine air management
conditions and engine operating conditions.
Description
RELATED APPLICATIONS/PRIORITY
[0001] This application contains subject matter related to that of
the following commonly-assigned applications: U.S. application Ser.
No. 13/068,679, filed May 16, 2011; PCT application US2013/026737,
filed Feb. 19, 2013; and U.S. application Ser. No. 13/782,802,
filed Mar. 1, 2013.
BACKGROUND
[0002] The field is two-stroke cycle internal combustion engines.
Particularly, the field relates to uniflow-scavenged,
opposed-piston engines with air handling systems that provide
pressurized charge air for combustion and process the products of
combustion. In some aspects, such air handling systems recirculate
and mix exhaust gas with the pressurized charge air in order to
lower combustion temperatures.
[0003] A two-stroke cycle engine is an internal combustion engine
that completes a power cycle with a single complete rotation of a
crankshaft and two strokes of a piston connected to the crankshaft.
One example of a two-stroke cycle engine is an opposed-piston
engine in which two pistons are disposed in opposition in the bore
of a cylinder for reciprocating movement in opposing directions.
The cylinder has longitudinally-spaced inlet and exhaust ports that
are located near respective ends of the cylinder. Each of the
opposed pistons controls one of the ports, opening the port as it
moves to a bottom center (BC) location, and closing the port as it
moves from BC toward a top center (TC) location. One of the ports
provides passage of the products of combustion out of the bore, the
other serves to admit charge air into the bore; these are
respectively termed the "exhaust" and "intake" ports.
[0004] In FIG. 1A, a two-stroke cycle internal combustion engine is
embodied by an opposed-piston engine 49 having at least one ported
cylinder 50. For example, the engine may have one ported cylinder,
two ported cylinders, three ported cylinders, or four or more
ported cylinders. Each cylinder 50 has a bore 52 and exhaust and
intake ports 54 and 56 formed or machined in respective ends of a
cylinder wall. Each of the exhaust and intake ports 54 and 56
includes one or more circumferential arrays of openings in which
adjacent openings are separated by a solid bridge. In some
descriptions, each opening is referred to as a "port"; however, the
construction of a circumferential array of such "ports" is no
different than the port constructions shown in FIG. 1A. In the
example shown, the engine 49 further includes two crankshafts 71
and 72. The exhaust and intake pistons 60 and 62 are slidably
disposed in the bore 52 with their end surfaces 61 and 63 opposing
one another. The exhaust pistons 60 are coupled to the crankshaft
71, and the intake pistons are coupled to the crankshaft 72.
[0005] As the pistons 60 and 62 of a cylinder 50 near TC, a
combustion chamber is defined in the bore 52 between the end
surfaces 61 and 63 of the pistons. Fuel is injected directly into
the combustion chamber through at least one fuel injector nozzle
100 positioned in an opening through the sidewall of a cylinder
50.
[0006] With further reference to FIG. 1A, the engine 49 includes an
air handling system 51 that manages the transport of charge air
provided to, and exhaust gas produced by, the engine 49. A
representative air handling system construction includes a charge
air subsystem and an exhaust subsystem. In the air handling system
51, the charge air subsystem includes a charge air source that
receives intake air and processes it into charge air, a charge air
channel coupled to the charge air source through which charge air
is transported to the at least one intake port of the engine, and
at least one air cooler in the charge air channel that is coupled
to receive and cool the charge air (or a mixture of gasses
including charge air) before delivery to the intake port or ports
of the engine. Such a cooler can comprise an air-to-liquid and/or
an air-to-air device, or another cooling device. The exhaust
subsystem includes an exhaust channel that transports exhaust
products from exhaust ports of the engine for delivery to other
exhaust components.
[0007] With further reference to FIG. 1A, the air handling system
51 includes a turbocharger 120 with a turbine 121 and a compressor
122 that rotate on a common shaft 123. The turbine 121 is coupled
to the exhaust subsystem and the compressor 122 is coupled to the
charge air subsystem. The turbocharger 120 extracts energy from
exhaust gas that exits the exhaust ports 54 and flows into an
exhaust channel 124 directly from the exhaust ports 54, or from an
exhaust manifold 125 that collects exhaust gasses output through
the exhaust ports 54. In this regard, the turbine 121 is rotated by
exhaust gas passing through it. This rotates the compressor 122,
causing it to generate charge air by compressing intake air. The
charge air subsystem includes a supercharger 110. The charge air
output by the compressor 122 flows through a charge air channel 126
to a cooler 127, whence it is pumped by the supercharger 110 to the
intake ports. Air compressed by the supercharger 110 can be output
through a cooler 129 to an intake manifold 130. The intake ports 56
receive charge air pumped by the supercharger 110, through the
intake manifold 130. Preferably, in multi-cylinder opposed-piston
engines, the intake manifold 130 is constituted of an intake plenum
that communicates with the intake ports 56 of all cylinders 50.
[0008] The air handling system shown in FIG. 1A is constructed to
reduce NOx emissions produced by combustion by recirculating
exhaust gas through the ported cylinders of the engine. The
recirculated exhaust gas is mixed with charge air to lower peak
combustion temperatures, which lowers NOx emissions. This process
is referred to as exhaust gas recirculation ("EGR"). The EGR
construction shown utilizes exhaust gasses transported via an EGR
loop external to the cylinder into the incoming stream of fresh
intake air in the charge air subsystem. The recirculated gas flows
through a conduit 131 under the control of a valve 138 (this valve
may also be referred to as the "EGR valve").
[0009] An example of a specific EGR loop construction (which is not
intended to be limiting) is the high pressure configuration
illustrated in FIG. 1B. In this regard, a high pressure EGR loop
circulates exhaust gas obtained from a source upstream of the input
to the turbine 121 to a mixing point downstream of the output of
the compressor 122. In this EGR loop, the conduit 131 and the EGR
valve 138 shunt a portion of the exhaust gas from the exhaust
manifold 125 to be mixed with charge air output by the compressor
122 into the conduit 126. If no exhaust/air mixing is required the
valve 138 is fully shut and charge air with no exhaust gas is
delivered to the cylinders. As the valve 138 is increasingly
opened, an increasing amount of exhaust gas is mixed into the
charge air. Conversely, from an open state, as the valve 138 is
increasingly closed, a decreasing amount of exhaust gas is mixed
into the charge air. This loop subjects the recirculated exhaust
gas to the cooling effects of the two coolers 127 and 129. If less
cooling is merited, the exhaust gas portion can be shunted around
the cooler 127 to the input of the supercharger 110; this
alternative subjects the exhaust gas portion to cooling by only the
charge air cooler 129. A dedicated EGR cooler that cools only
exhaust gas can be incorporated into the conduit 131, in series
with the valve 138, or in series with the output port of the valve
138 and the input to the supercharger 110.
[0010] As per FIG. 1B, a control mechanization to operate the air
handling system of a two-stroke cycle opposed-piston engine
includes an ECU 149. The ECU controls the amount of exhaust gas
mixed with the pressurized charge air in response to specified
engine operating conditions by automatically operating the valves
138 and 139 (and, possibly other valves), the supercharger 110, if
a multi-speed or variable speed device is used, and the
turbo-charger 120, if a variable-geometry device is used. Of
course, operation of valves and associated elements used for EGR
can include any one or more of electrical, pneumatic, mechanical,
and hydraulic actuating operations. For fast, precise automatic
operation, it is preferred that the valves be high-speed,
computer-controlled devices with continuously-variable settings.
Each valve has a state in which it is open (to some setting
controlled by the ECU 149) to allow gas to flow through it, and a
state in which it is closed to block gas from flowing through
it.
[0011] In a two-stroke cycle opposed-piston such as is illustrated
in FIGS. 1A and 1B, the supercharger is used to create a positive
pressure differential across the engine in order to drive the
airflow and EGR flow. In addition to supercharger, a turbocharger
is used to extract some of the exhaust gas energy heat for driving
the compressor on the intake side so as to increase the density of
the air entering the supercharger, thus reducing the volume flow
and pressure ratio through the supercharger. These air handling
constructions for two-stroke cycle opposed-piston engines have
emphasized positive objectives such as management and effective
delivery of charge air and/or control of the transport and mixing
of exhaust gas in the charge air delivered for combustion.
[0012] However, as the designs of opposed-piston engines continue
to evolve for applications in modern transportation systems, air
handling systems for those engines must increasingly contribute to
improved performance. Accordingly, it is desirable to equip
opposed-piston engines with improved air handling constructions
that reduce fuel consumption, improve transient response and
controllability in the face of changing operating conditions, and
improve external EGR driving capability, without increasing
mechanical loads on the engine.
SUMMARY
[0013] A two-stroke cycle opposed-piston engine has an air handling
system equipped with a turbo-compound system. In this regard, a
turbo-compound system includes a blowdown turbine (also called a
"blowdown power turbine") that produces a rotary-mechanical output
in response to a flow of exhaust gas flowing into the turbine. The
rotary-mechanical output is coupled to a rotating element of the
engine. The turbo-compounding system recovers energy from the
exhaust gas and couples the recovered energy back into the engine,
thereby reducing the engine's specific fuel consumption.
[0014] In some aspects, the rotary-mechanical output is coupled to
an interlinked crankshaft system of the engine; in other aspects,
the rotary-mechanical output is coupled to a crankshaft of the
engine; in yet other aspects, rotary-mechanical output is coupled
to an electrical converter of the engine.
[0015] In some aspects, the air handling system includes both a
turbocharger and supercharger, and exhaust gas is provided to the
blowdown turbine in parallel with the turbocharger input. In some
other aspects, the blowdown turbine is connected in series with the
turbine output of the turbocharger.
[0016] In some aspects, the air handling system includes a
supercharger but no turbocharger. In these cases, the blowdown
turbine receives the flow of exhaust gas in parallel with the EGR
loop.
[0017] In some further aspects, the air handling system includes a
supercharger but no turbocharger and no EGR loop. In these cases,
the power turbine receives the entire flow of exhaust gas.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1A is a diagram of an opposed-piston engine equipped
with an air handling system with EGR and is properly labeled "Prior
Art".
[0019] FIG. 1B is a schematic drawing illustrating a control
mechanization for regulation of an air handling system in an
opposed-piston engine.
[0020] FIG. 2 is a schematic drawing illustrating an opposed-piston
engine with a first air handling system construction including a
first arrangement of a turbo-compound system.
[0021] FIG. 3 is a schematic drawing illustrating an opposed-piston
engine with the first air handling system construction including a
second arrangement of a turbo-compound system.
[0022] FIG. 4 is a schematic drawing illustrating an opposed-piston
engine with the first air handling system construction including a
third arrangement of a turbo-compound system.
[0023] FIG. 5 is a schematic drawing illustrating an opposed-piston
engine with the first air handling system construction including a
fourth arrangement of a turbo-compound system.
[0024] FIG. 6 is a schematic drawing illustrating an opposed-piston
with the first air handling system construction including a fifth
arrangement of a turbo-compound system.
[0025] FIG. 7 is a schematic drawing illustrating an opposed-piston
engine with the first air handling system construction including a
sixth arrangement of a turbo-compound system.
[0026] FIG. 8 is a schematic drawing illustrating an opposed-piston
engine with a second air handling system construction including a
first arrangement of a turbo-compound system.
[0027] FIG. 9 is a schematic drawing illustrating an opposed-piston
engine with the second air handling system construction including a
second arrangement of a turbo-compound system.
[0028] FIG. 10 is a schematic drawing illustrating an
opposed-piston engine with a third air handling system construction
including a turbo-compound system.
[0029] FIG. 11 is a side elevation view of an arrangement of
cylinders, pistons, and crankshafts in an opposed-piston engine
equipped with a turbo-compound system.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0030] Various different air handling system constructions for a
two-stroke cycle opposed-piston engine are described, all of which
use a turbo-compound system in combination with a supercharger. For
example, in FIG. 1B, the air handling system of the two-stroke
cycle opposed-piston engine is equipped with the supercharger 110
and a blowdown turbine 210 that receives some portion of the
exhaust gas flowing in the conduit 124 and produces a
rotary-mechanical output. In some aspects, such air handling system
constructions may include a turbocharger. In any case, the
turbo-compound system converts exhaust energy into
rotary-mechanical power that is coupled back into a rotating
element of the engine, thus reducing the fuel required to generate
desired engine power.
[0031] In some aspects, depending on operating conditions and
selection of components, the combined efficiency of a
turbo-compound system together with a turbocharger/supercharger
combination has the potential to be greater than the efficiency of
an air handling system with only a turbocharger/supercharger
combination.
[0032] Preferably, the turbo-compound system is equipped with a
bypass valve to regulate the flow of exhaust gas through the
blowdown turbine, which can be useful in controlling the exhaust
pressure of the engine, an important control parameter. Such
regulation is also useful to control the mass flow through, or the
pressure drop across, the engine and thus the speed of the
turbocharger turbine. The ability to increase the exhaust pressure
by regulating the flow of exhaust gas through the blowdown turbine
can also help increase the external EGR driving pressure
difference, thus giving better control of engine emissions. In the
air handling constructions to be described in detail, the bypass
valve is a computer controlled device that is connected to an air
handling system control mechanization operable to control air
handling system components as described above in connection with
FIG. 1B in response to air management inputs and engine operating
conditions.
[0033] In those air handling constructions including a turbocharger
and a supercharger, the blowdown turbine is situated in the exhaust
channel in series with, or parallel to, the turbocharger turbine.
In some aspects, the rotary mechanical output produced by the
blowdown turbine is coupled to an engine gear train, a supercharger
driving gear, or an electrical energy device.
[0034] With reference to FIGS. 2, 3, and 4, an air handling system
such as that illustrated in FIGS. 1A and 1B is equipped with a
turbo-compounding system 200 including a blowdown turbine 210
having a turbine input 211, a turbine output 212, and a
rotary-mechanical output 213. The blowdown turbine 210 can be an
axial-flow or a radial-flow device. The turbine input 211 is
coupled to the output of the turbine 121. The turbine output 212 is
coupled to an exhaust output channel 215. Preferably, the exhaust
output channel 215 includes one or more after treatment (AT)
devices through which exhaust gas flows out of the engine. The
blowdown turbine is shunted by a bypass valve 220 connected between
the turbine input 211 and the turbine output 212. The supercharger
110 is driven by the interlinked crankshaft system 250 via a gear
251.
[0035] As per FIG. 2, the rotary-mechanical output 213 of the
blowdown turbine 210 is coupled via a fluidic coupling 214 to a
rotating element of the engine 49. In some aspects the rotating
element is an element of an interlinked crankshaft system 250 with
which the crankshafts 71 and 72 are coupled. Preferably, the
rotating element is one of the crankshafts 71 and 72.
[0036] With reference to FIG. 3, the air handling system is
constructed in the same manner as in FIG. 2, except that the
rotary-mechanical output 213 of the blowdown turbine 210 is coupled
directly by a gear 252 to the gear 251 that drives the supercharger
110.
[0037] With reference to FIG. 4, the air handling system is
constructed in the same manner as in FIG. 2, except that the
rotary-mechanical output 213 of the blowdown turbine 210 is coupled
directly by an electrical drive system including a generator 260, a
battery 262, and electric motor 263 to directly drive the
supercharger 110.
[0038] With reference to FIGS. 5, 6, and 7, an air handling system
such as that illustrated in FIGS. 1A and 1B is equipped with a
turbo-compounding system 200 including a blowdown turbine 210
having a turbine input 211, a turbine output 212, and a
rotary-mechanical output 213. The blowdown turbine 210 can be an
axial-flow or a radial-flow device. The turbine input 211 is
coupled to the exhaust channel 124 in common with the input of the
turbine 121. The turbine output 212 is coupled to the exhaust
output channel 215 in common with the output of the turbine 121.
Thus, the blowdown turbine 210 is coupled to the exhaust channel in
parallel with the turbine 121. The bypass valve 220 is coupled in
series with the turbine input 211. The supercharger 110 is driven
by the interlinked crankshaft system 250 via the gear 251.
[0039] In FIGS. 5, 6, and 7, the rotary output 213 of the blowdown
turbine is coupled to rotating elements of the engine 49 in the
same manner as in FIGS. 2, 3, and 4, respectively.
[0040] With reference to FIGS. 8, 9, and 10, an air handling system
with no turbocharger is equipped with a turbo-compounding system
200 including a blowdown turbine 210 having a turbine input 211, a
turbine output 212, and a rotary-mechanical output 213. The
blowdown turbine 210 can be an axial-flow or a radial-flow device.
The turbine input 211 is coupled to the exhaust channel 124. The
turbine output 212 is coupled to the exhaust output channel 215.
The supercharger 110 is driven by a continuously variable
transmission (CVT) that is rotatably coupled to the interlinked
crankshaft system 250 via the gear 251. In FIGS. 8, 9, and 10, the
turbine output 213 is coupled to the crankshaft system 250 by a
gear 256. In FIG. 9, the bypass valve 220 shunts the input 211 of
the blowdown turbine to the exhaust output channel 215. In FIG. 10,
the air handling system is without an EGR loop.
[0041] Turbo-Compound System with a Supercharger:
[0042] In the air handling system constructions of FIGS. 2, 3, 5,
and 6, the supercharger work is greater than in the air handling
system shown in FIGS. 1A and 1B, but there is a potential to
improve the overall system efficiency. This is due the fact that
the efficiency of hydraulic coupling 214 or direct mechanical
coupling 251 is better than that of a compressor, resulting in
better utilization of turbine power, and the supercharger
efficiency is better due to an increase in pressure ratio demand
(enabled by 214 or 251) for the same amount of mass flow. Those
cases in which the rotary mechanical output of the blowdown turbine
is coupled directly to a gear driving the supercharger result in a
reduction in mechanical loads on the gears connecting the
supercharger to the engine crankshafts, thus reducing the weight of
the gear train.
[0043] In the air handling system constructions of FIGS. 4 and 7,
exhaust gas power is drawn from the blowdown turbine 210 and
provided to the supercharger 110 by converting the mechanical
energy produced by the blowdown turbine into electrical energy used
to drive the supercharger. In these cases the supercharger 110 is
driven electrically and is not directly connected to the crankshaft
system 250. The turbo-compound system 200 drives the generator 260,
which charges the power source 262 for the supercharger motor
263.
Turbo-Compound System with a Turbocharger and a Supercharger:
[0044] Series Configuration: The air handling system constructions
of FIGS. 2, 3, and 4 place the turbo-compound system 200 in series
with the turbocharger turbine 121 so as to harvest additional
energy from the exhaust gas before it enters the after treatment
devices. In the constructions of FIGS. 2 and 3, the additional
energy is added to the crankshaft system 250. In the construction
of FIG. 4, the additional energy is applied directly to drive the
supercharger 110. The supercharger work requirement is greater in
these air-handling constructions than in the conventional case
illustrated in FIG. 1A because of lower work from the turbine 121
and compressor 122, but the additional supercharger work is less
than the additional power produced by the blowdown turbine 210,
resulting in improved overall system efficiency. Connecting the
blowdown turbine in series with the turbocharger turbine reduces
the chance of compressor choking (when the compressor pressure
ratio is low and mass flow is high) when higher power is required
during the transient because the mass flow of exhaust gas through
the turbocharger turbine is not reduced when the blowdown turbine
210 is bypassed keeping the compressor pressure ratio higher.
[0045] Under control of the air handling system control
mechanization of FIG. 1B, the bypass valve 220 of the blowdown
turbine 210 can be closed to: force the exhaust gas to pass through
the blowdown turbine 210, thereby increasing the exhaust pressure;
increase the EGR driving pressure difference; and/or prevent the
turbine 121 from over speeding when its mass flow and pressure
ratios are high. Opening the bypass valve 220 also enables
reduction of the exhaust pressure so as to increase the pressure
difference across the engine 49, which improves scavenging
efficiency in the cylinders, allowing more trapped fresh air in the
cylinders to produce more power. The bypass valve 220 can also be
opened to reduce the piston temperatures in cases of overheating by
improving the scavenging efficiency. Further, the bypass valve 220
can be opened to increase the temperature of the exhaust gases
entering into the after treatment, which improves the efficiency of
the after treatment devices.
[0046] Parallel Configuration: The air handling system
constructions of FIGS. 5, 6, and 7 place the turbo-compound system
200 in parallel with the turbocharger turbine 121. The portion of
the exhaust gas not diverted for EGR ("engine out exhaust") is
apportioned between the turbine 121 and the blowdown turbine 210.
Per FIGS. 5 and 6, the blowdown turbine 210 converts the exhaust
energy into mechanical power, but instead of driving the compressor
122, it passes this power to the crankshaft system 250 through 251
or 252. In the construction of FIG. 7, the additional energy is
applied directly to drive the supercharger 110. The supercharger
work requirement is greater with this air-handling architecture
than in the conventional case seen in FIG. 1A because of lower work
from the turbine 121 and the compressor 122, but the additional
supercharger work is less than the additional power produced by the
blowdown turbine 210, resulting in improved overall system
efficiency. The bypass valve 220 controlling the flow of exhaust
gas can be placed before or after the blowdown turbine 210; in
either case the bypass valve/blowdown turbine series combination is
parallel to the turbine 121. However, placing the bypass valve 220
after the blowdown turbine 210 reduces the temperature of the
exhaust gas entering the valve because of temperature drop through
the blowdown turbine, which is an advantage for better durability
of the valve. Also, in providing hotter exhaust gas to the blowdown
turbine 210 makes more of the exhaust energy available to the
blowdown turbine for conversion into mechanical work.
[0047] Under control of the air handling system control
mechanization of FIG. 1B, the bypass valve 220 of the blowdown
turbine 210 can be closed to: reduce the power produced by the
blowdown turbine 210; increase the exhaust pressure by forcing the
exhaust gas to pass through the turbine 121; and/or increase the
EGR driving pressure difference in the case of a high pressure EGR
circuit. The same valve 220 can be opened to: reduce the exhaust
pressure by increasing the flow through the blowdown turbine 210;
increase pressure difference across the engine that improves
scavenging efficiency in the cylinders, allowing more trapped fresh
air in the cylinders to produce more power; reduce the piston
temperatures in case of overheating by improving scavenging
efficiency; prevent the turbine 121 from over speeding by reducing
the mass flow and pressure difference across it; and/or increase
the temperature of the exhaust gases entering into the after
treatment, a critical requirement to improve the efficiency of the
after treatment devices.
[0048] Air Handling System Constructions without a
Turbocharger:
[0049] The air handling system constructions of FIGS. 8, 9, and 10
do not include a turbocharger. Instead, the crankshaft-driven
supercharger 110 generates the positive pressure differential
across the engine 49 necessary to drive the flow of charge air and
recirculate exhaust gas. Conversion of exhaust gas energy to
rotary-mechanical motion is performed exclusively by the blowdown
turbine 210. The absence of the turbocharger significantly
increases the pumping work of the supercharger 110; therefore, the
addition of the blowdown turbine 210 is desirably offsets energy
expended in operating the supercharger 100. Addition of the bypass
valve 220 (FIG. 9) affords the opportunity to regulate exhaust
temperature and pressure under control of the air handling system
control mechanization of FIG. 1B. If the application requires
variable back pressure or if one fixed blowdown turbine does not
meet performance requirements throughout the entire operating range
of the engine, then a variable geometry blowdown turbine can be
used. Alternately, an exhaust throttle can be used in conjunction
with a fixed geometry blowdown turbine to meet backpressure
requirements for EGR flow.
[0050] After Treatment Considerations:
[0051] With reference to FIGS. 2-10, it is possible to have
specific after treatment configurations with the above shown air
handling constructions based on particular applications. The
temperatures of exhaust gas coming out of an exhaust manifold are
expected to be lower in a two-stroke cycle opposed-piston engine as
compared to conventional four-stroke diesel engines. A baseline
arrangement is shown in FIGS. 8-10 wherein a diesel oxidation
catalyst device (DOC), a selective catalytic reduction device
(SCR), and a diesel particulate filter device (DFR) are arranged in
sequence following the output of the blowdown turbine 210. In some
aspects, the performance of the SCR can be improved if it is placed
between the DOC and DPF, which will assist in faster light-off for
the SCR catalyst. The DOC is positioned in front (upstream) of the
SCR in order to oxidize some of the NO to NO2 for better SCR
performance. This configuration is particularly well suited to
after treatment following a fixed-geometry turbocharger with a
waste gate or a blowdown turbine without a turbocharger. In other
configurations, a DOC-SCR system is placed between the engine 49
and the turbo machinery; a particulate matter reduction system
including a DOC-DPF configuration is placed after the turbo
machinery. It is also possible to place a DOC-DPF system in front
of the turbo machinery. Another approach to control NOx is to use a
lean NOx trap (LNT) in conjunction with a non-urea SCR. It should
also be noted that the after treatment components--DOC, DPF, SCR,
LNT, and, possibly, others--can be placed in various different ways
and combinations with a turbocharger and turbo-compound system.
Some or all of these devices can be placed between the turbine 121
and the blowdown turbine 210 in the case of a turbo-compound system
in series with the turbine 121. In the parallel case (FIGS. 5, 6,
and 7) however, the after treatment components have to be either
installed before the split of the exhaust mass flow in two branches
or after these branches are combined again, in order to provide the
chemical treatment to all of the exhaust mass flow.
[0052] Coupling Embodiment:
[0053] We now describe one embodiment for coupling rotary output of
a blowdown turbine to a rotating element of an opposed-piston
engine. This embodiment is merely for illustration, and is not
meant to be limiting.
[0054] FIG. 11 is a partially schematic representation of an
arrangement of cylinders, pistons, and crankshafts in an
opposed-piston engine equipped with a blowdown turbine. The figure
shows a three-cylinder arrangement, although this is not intended
to be limiting; in fact, a blowdown turbine be applied to air
handling systems of opposed-piston engines with fewer, or more,
cylinders. As per the example of FIG. 1A, the opposed-piston engine
includes cylinders 50 (or sleeves or liners), each including
exhaust and intake ports 54 and 56. Preferably, the cylinders are
fixedly mounted to an engine frame or block (not shown). In this
engine construction, a pair of pistons (unseen in this figure) is
disposed for opposing reciprocal movement in the bore of each
cylinder 50. One piston of each pair is coupled to a respective
crank journal 73 of the crankshaft 71 by a connecting rod assembly
57; the other piston is coupled to a respective crank journal 75 of
the crankshaft 72 by a connecting rod assembly 59.
[0055] An opposed-piston engine corresponding to FIG. 11 includes
an interlinked crankshaft system including two rotatably-mounted
crankshafts 71 and 72 disposed in a parallel spaced-apart
configuration and a gear train assembly 250 linking the crankshafts
and coupling them to an output shaft (not shown). Preferably, the
crankshafts are co-rotating, although a counter-rotating
arrangement can be provided by deletion of one gear from (or
addition of another to) the gear train assembly 250. FIG. 11 shows
an exemplary embodiment for coupling the blowdown turbine 210 to
the crankshaft 71 and the supercharger 110 through gears 252, 251,
and 270 (although a belt can be used as well). In this embodiment
(which is not intended to be limiting) the blowdown turbine 210 is
coupled directly to the supercharger 110 by gears 252 and 251. With
this coupling, the gear ratio between the higher speed turbine 210
and the low speed crankshaft 72 can be better managed by having the
medium speed supercharger 110 in the middle. For example, the
engine speed can be 2000 rpm; supercharger speed can be
5*2000=10000 rpm; and compounded turbine speed can be
8*10000=800000 rpm. This requires one idle gear between engine and
compounded turbine to manage such a high ratio of speed; the
supercharger 110 in the middle serves as the idle gear. The
mechanical losses of the power transmission can be lower since the
supercharger 110 is the power consuming device and blowdown turbine
210 is the power producing device. Thus, only the additional
supercharger work that cannot be covered by the power producing
blowdown turbine has to be transmitted between engine, crankshaft
71, and the supercharger 110. This could mean lower thickness gears
251 and 270 (or using lower strength materials) between the
crankshaft and the supercharger. In case the blowdown turbine 210
produces more power than what the supercharger 110 requires, this
additional power will get transmitted back to the crankshaft
through these gears.
[0056] Although air handling constructions have been described with
reference to an opposed-engine with two crankshafts, it should be
understood that these constructions can be applied to
opposed-piston engines with one or more crankshafts. Moreover,
various aspects of these constructions can be applied to
opposed-piston engines with ported cylinders disposed in
opposition, and/or on either side of one or more crankshafts.
Accordingly, the protection afforded to these constructions is
limited only by the following claims.
* * * * *